Process and apparatus for the production of aluminum oxide



March 1958 R. w. DINGMAN ET AL 2,828,186

PROCESS AND APPARATUS FOR THE PRODUCTIONfOF ALUMINUM OXIDE Original Filed Dec. 2, 1952 United States Pate t .I2',8Z818'6.. YRfiCESS -KND *AZPPARATUS FGR THE PRDUG- 'TIGN 0F Robert vW' lDingman, rPampa, andiLaurent P. lMi ch'el, Houston, .Tex.,fand William D."Shaefl?er, Coopers burg, "Pa., assignorsto Godfrey L.'Cabot,lnc., Boston, Mass,

a corporation of Massachusetts IGontinuafitmgbf:application Serial No. 323 682, 13866111- ber z, 1952. This application March 2,4956, serial N0i-569,,113'

"8 Claim's. (IHild -"142) I H his invention 'srelates "to ithe production of lfinely -'-divided;aluminum' oxide froin aluminum sulfate. M-ore -particularly; it comprises:a new and im'provedprocesslfor produeing finelynivided aluminum o'xide-andsulfur oxiiles from hydrated aluminum sulfate containing 6 or rn'o're molecules of water per molecule of aluminum sulfate.

"=The inve'ntion includes within its scope-novel apparatus by which the said process may be advantageously 'c'ar- *ried out.

"An import-ant advantage of'the process of" this invention overprocesses-heretofore knownis -that the commercially availa'ble hydrated aluminum sulfate can be used =-Without alteration as-the raw-material. ln p'rior'p'rocess'es ithas' been e'ssential, in order to produce a finely divided aluminum oxide, todehydrate "the "raw materialunder "vacuum. "Without'that preliminary step the sulfate melts continuousiprocess "for converting the-sulfateof aluminum "totheoxide'inthepractice of whichitheoxides of'sulfur may be rapidlyremove'd from the reaction "zone and "thef'formation -ofSO thus'keptto a'minimu'm.

It is a further object of this-invention to proVide an apparatus in which hydrated aluminum.sulfate can be continuously and'cfliciently converted to the oxide.

Broadly, the process of this inventionconsiststin the steps of continuouslyiintroducing hydrated aluminum sulfate as a moltenspray or in -solid particulate form into' a heated reactionzonezmaintained atJ-a-temperature'abOVe 770 C. and preferably below :-'about 1100 C., continuously removing the gaseous decomposition pro'ductsi'therefrom as they are formed-retaining the solidi-produc't therein for a time sufiicient to remove substantially all'df the undecornposed aluminum sulfate remaining admixed therewith after the initial reaction and recovering the alurni'num o'xide lproduct. Additional'. steps 1 include .passing-='th'e gaseous decomposition products having sulfate fines sus'pended thereintthrough a cyclone separator, recycli'rigithe separated 'fines to the reaction :zone and con- 'ductin'g the gas'es to a sulfur recoveryzone. The alumi- *num 'oxi'de prod-uct is withdrawn .from the rreaction :zone 7 i'nt'err'nitteritly or co'ntinuously as expedient :and while in *tlie reaction 'zo'ne may further be mechanically agitated to improve hea't transfer. The aluminum :sulfate 'raw 'mate'rial may be introduced into: the reaction zone either as a solid or as} a liquid.

'"Ihisinvention' will best be understood and appreciated ifr'om the following description of the process andapparatus illustrated "in theraccompanying :drawings: in which '-'ing theliquids. =A portionoff'the liquids ma-y be recycled through line 30 if desired. The 'exhaust' gases are removed by afan=32 and discharged into a'stack 3'4. A cooling device '(n'ot shown) l1 may he =pr'ovi'ded in -eonduit -22 if desired.

The reactor of this invention'in' which the process of thisinvention rnay conveniently be earried out isshown in detail in Fig.2. lt'consis'ts' df 'a furna'ce 4'0' lined'with refractory material "42 and having arefra'ctory tube 44 positioned vertically therein. Burners ldareprovided to -"fireinto the furnace, 'p'referab'ly'in'a direction tangent to the inner wall thereo'f. A fiue-48"provides for the escape of combustion product gases which may be utilized 10 heat 'cyclone 1 8 and the exhaustfanfii to'prevent condensation of'inoisture therein. 7 v

"The refractorytube 4'4whiehmay alsobe referred *to as the reaction" tube, extendsthrough the furnace '40 'andis heated by "the--flan1e fromburners 16. The upper "end of the tube is' covered 'by 'a ;p'late4'9 having openings to which are connected feed' pipe l-i'an d "gas'discharge pipe 16. The bottom end of tube -44is'preferablya tapered section" 50 "in? which 'a'rplug 52'- may vbe'seated to prevent escape "of "solid productf"from theheated "zone. Plug'52' issupportedby'ro d54 arrangedfor 'both" rotation and vertical travel in 'productidisch'arge"pipe 14. Plug 50 may advantageously have vanes I56 r'attached' to its upper surface which "s'erv'eto' agitatethebed for" solid product when rod 54 is. rotated.

Secured to the under surface or cover plate .49 is a cylindrical baffle "58' extending part-way .into"tuhe 44. It" is advantageously "employed" to prevent short Qcircuiting of the system which might tend to cause 'an excessive amountof raw materialto be--carr-ied-out ofthe-tube through discharge pipe 16. ,Even with baflle 58 in: place solid fines of the hydrated sulfate -will--to -someextent be :carried out:.in.-.-the by -product gases and-.vmust befiecovered-in separator18.

Becausethe section of'feed pipeflzcclose tor-reaction tube 44 would otherwisebecome-hotiand'cause' the alurninum sulfate rawzmaterial' to adhere totitsawall'sia=coo1ing jacket 60-is advantageously employed arounti lthe feed pipe. Cooling fluid'is circulated therethrough in the usual manner. Other means of cooling known to those skilled in the art may be employed as well. If the aluminum sulfate is introduced as a moltenspray "a heating fluid 'may be circulatedthroug'h 'jacket'Gtl.

Although plug "52 will ordinarily aserve *to'controlithe removal ofsolid productfrorn reac'tion'tube- 44 additional control means may be provided. Asillustrated ava'lve "62 is included .inithe product discharge pipeand when closed will permit the raising of plug '52 without allowing .any of the product to escape.

The processis. carried out asfollowszIHydrated aluminum sulfate is continuously fed: at a controlled rate throughfeedpipe 12'and bathe-58. :Asnthesulfateienters the :hot' reaction zone its paritcles explode-t asthersulfate is first dehydrated and then decomposed: tor-aluminum .2, 1952, now abandoned.

oxide, which drops to the bottom of reaction tube 44, and to oxides of sulfur, oxygen and steam which flow upwardly out of the reactor through flue 16. The solid product is retained in the bottom of the reaction tube 44 until substantially all of the aluminum sulfate remaining admixed therewith is decomposed. After the process has been carried out long enough to provide an accumulation of aluminum oxide this product is withdrawn from the bottom of the bed at a controlled rate so that the residence time will be uniform for all of the product.

Since the sulfate raw material will contain fines the byproduct gases are preferably passed through cyclone sepparticle size of the resulting solid product may be accurately controlled by suitable regulation of the raw material feed rate, temperature within the reaction tube and residence time of the product in the bottom of the tube. Products of differing properties may be produced by varying the above operating conditions.

Feed tube 12 may be supplied by any convenient means as through a closed conduit having a rotary valve, or, in an open system, from a vibratory or belt conveyor and the like.

Alternatively, the aluminum sulfate may be introduced into reaction tube 44 in the molten state. In such case feed tube 12 will terminate within the reactor in suitable spray nozzles and the feed reservoir will be heated.

Jacket 60 may then be used to conduct hot rather than cold fluid, or other feed tube heating means may be employed or external heating may be omitted entirely. The advantage of spraying the material into the reactor as a liquid of course lies in the small size of the spray droplets which are considerably smaller than the solid particles. The smaller the size of the sulfate increments the greater will be the heat transfer efficiency to reduce the amount of sulfate remaining on the aluminum oxide immediately following the initial decomposition reaction.

In the following example are set forth data derived from several runs made according to the process of this invention in which the aluminum sulfate hydrate was in solid particulate form, the particles being no larger than about mesh in size.

Having thus disclosed our invention, and described in detail a preferred embodiment thereof, we claim and desire to secure by Letters Patent:

1. A process for the production of aluminum oxide from aluminum sulfate which comprises the steps of introducing hydrated aluminum' sulfate in solid particulate form including fines at a controlled rate into the upper end of an elongated, vertically disposed reaction zone heated externally to an internal temperature above. the decomposition temperature of aluminum sulfate, thereby decomposing the aluminum sulfate to aluminum oxide and gaseous oxides of sulfur and liberating the water therefrom as the sulfate flows by gravity through' s'aid reaction zone, removing the gaseous oxides and 'water vapor from the upper end of said zone, collecting the solid aluminum oxide in the lower end of said zone out of contact with said gaseous oxides and water vapor, heating the aluminum oxide thereinin a substantially moisture-free atmosphere to decompose the major portion of the sulfate remaining adsorbed thereon, recovering the aluminum oxide, and recycling the fines to the reaction zone.

2. ,The process of claim 1 in which the aluminum sulfate is introduced into the reaction zone as a spray in liquid'form. V V

3. The process of'claim 1 in which the temperature in the reaction zone is between about 770 C. and 1100 C.

4. The process of claim 1 in which the aluminum sulfate is delivered to the reaction zone at a point substantially distant fromthe point of gaseous oxides withdrawal.

5. The process of claim 1 further characterized by conducting the gaseous oxides through a separation zone, therein separating the entrained solids from the gaseous oxides, and recycling thesolids to the reaction zone.

6. The process of claim 1 in which the solid product is retained in the lower end of the reaction zone for 30-120 minutes. 7

7. Apparatus for the production of aluminum oxide from hydrated aluminum sulfate, comprising a vertically disposed furnace enclosing an elongated refractory reactor, an inlet connection for the sulfate and a gas outlet connection both located in the upper end of the reactor, connections to said inlet for admitting recirculated fines to the reactor,a cylindrical bafile axially aligned with said inlet and extending downwardly as an extension thereof into the reactor for a substantial distance, thus preventing the sulfate from escaping directly to the outlet connection, and an outlet for solid aluminum oxide in the bottom of the reactor. r

Run No 4 5 7 s 9 1o 11 1a V67 01 Wt. of feed (grns.) 130. 9 52?. 603 341. 9 603 603 603 603 Time to feed (mins) 40 28% 29 45 30 92 102 A120: residence in reactor (mins.) 60 88% 89 V 85 60 .120 Wt. of A1203 prod. (gms.)

, 16. 4 75. 3 86.3 50. 4 7a. 4 75. 4 73.1 86. 7 Yield percent of theoretieal. 75 86 8 72 73. 9 71. 7 83. 8 Reaction zone temp., 0 920 1, 030 1,080 1,085 1,135 1, 060 1, 075 ,940 Surf. area of A1203 (ME/gm.) 108 86. 2 88. 2 83.8 60. 2 121 143 Sulfate remaining on A1203, percent by wt- 2. 94 0.38 0.00 0.24 0.00 0.00 0. 00 4. 76 Density, lbs/cu. ft 2. 62 2. 76 2. 50 3. 20 2.83 2. 40 2. 10

Run V6 was made with a 94.4% dehydrated aluminum 8. A process for the production of aluminum oxide sulfate as the raw material. It will be noted that a much from aluminum sulfate which comprises the steps of higher bulk density is achieved when the raw material downwardly directinghydrated aluminum sulfate n solid is first dehydrated but that a longer residence time in the particulate form at a controlled rate lnto the upper end reactor is required, the surface area 'of the product is of an elongated, vertically disposed reaction zone heated lower than that of the hydrate products and the sulfate externally to an internal temperature above the decomremaining on the oxide is high considering the residence position temperature of aluminum sulfate, thereby decomim i 70 posing the aluminum sulfate to aluminum oxide and Run G1 representsaluminum oxide produced by roasting dehydrated aluminum sulfate in a kiln. The surface area of the produce is comparatively low. 7

This application is filed as a continuation of our copending application Serial No. 323,682, filed December gaseous oxides of sulfur and liberating the water therefrom as the sulfate flows by gravity through said reaction zone, removing the gaseous oxides and water vapor from the upper end of said zone, collecting the solid aluminum oxide in the lower end of said zone out of contact with said gaseous oxides and water vapor, heatingthe aluminum oxide therein in a substantially moisture-free at- References Cited in the file of this patent mosphere to decompose the major portion of the sulfate remaining admixed therewith after the initial reaction, UNITED STATES PATENTS and recovering the fine aluminum oxide thus produced. 1,132,736 Schwahn 23, 1915 5 1,652,119 Halvorsen et a1 Dec. 6, 1927 2,155,119 Ebner Apr. 18, 1939 2,402,471 Tuwinner et a1. June 18, 1946 2,431,370 Chirnside et a1 Nov. 25, 1947 

1. A PROCESS FOR THE PRODUCTION OF ALUMINUM OXIDE FROM ALUMINUM SULFATE WHICH COMPRISES THE STEPS OF INTRODUCING HYDRATED ALUMINUM SULFATE IN SOLID PARTICULATE FORM INCLUDING FINES AT A CONTROLLED RATE INTO THE UPPER END OF AN ELONGATED, VERTICALLY DISPOSED REACTION ZONE HEATED EXTERNALLY TO AN INTERNAL TEMPERATURE ABOVE THE DECOMPOSITION TEMPERATURE OF ALUMINUM SULFATE, THEREBY DECOMPOSING THE ALUMINUM SULFATE TO ALUMINUM OXIDE AND GASEOUS OXIDES OF SULFUR AND LIBERATING THE WATER THEREFROM AS THE SULFATE FLOWS BY GRAVITY THROUGH SAID REACTION ZONE, REMOVING THE GASEOUS OXIDES AND WATER VAPOR FROM THE UPPER END OF SAID ZONE, COLLECTING THE SOLID ALUMINUM OXIDE IN THE LOWER END OF SAID ZONE OUT OF CONTACT WITH SAID GASEOUS OXIDES AND WATER VAPOR, HEATING THE ALUMINUM OXIDE THEREIN IN A SUBSTANTIALLY MOISTURE-FREE ATMOSPHERE TO DECOMPOSE THE MAJOR PORTION OF THE SULFATE REMAINING ADSORBED THEREON, RECOVERING THE ALUMINUM OXIDE, AND RECYCLING THE FINES TO THE REACTION ZONE. 